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Date: Fri, 30 Mar 2012 20:43:26 +0000 (UTC)
From: "Sean Bridges (Commented) (JIRA)" <jira@apache.org>
To: dev@lucene.apache.org
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Subject: [jira] [Commented] (LUCENE-3932) Improve load time of .tii files
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    [ https://issues.apache.org/jira/browse/LUCENE-3932?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13242721#comment-13242721 ] 

Sean Bridges commented on LUCENE-3932:
--------------------------------------

{quote}Seems like if we made a direct "decode tii file and write in-memory format" (instead of going through SegmentTermEnum), we could get some of this back. The vLongs unfortunately need to be decoded/re-encoded because they are deltas in the file but absolutes in memory. But, eg the vInt docFreq could be a "copyVInt" method instead of readVInt then writeVInt, which should save a bit.{quote}

Is the space savings of delta encoding worth the processing time?  You could write the .tii file to disk such that on open you could read it straight into a byte[]
                
> Improve load time of .tii files
> -------------------------------
>
>                 Key: LUCENE-3932
>                 URL: https://issues.apache.org/jira/browse/LUCENE-3932
>             Project: Lucene - Java
>          Issue Type: Improvement
>    Affects Versions: 3.5
>         Environment: Linux
>            Reporter: Sean Bridges
>         Attachments: LUCENE-3932.trunk.patch, perf.csv
>
>
> We have a large 50 gig index which is optimized as one segment, with a 66 MEG .tii file.  This index has no norms, and no field cache.
> It takes about 5 seconds to load this index, profiling reveals that 60% of the time is spent in GrowableWriter.set(index, value), and most of time in set(...) is spent resizing PackedInts.Mutatable current.
> In the constructor for TermInfosReaderIndex, you initialize the writer with the line,
> {quote}GrowableWriter indexToTerms = new GrowableWriter(4, indexSize, false);{quote}
> For our index using four as the bit estimate results in 27 resizes.
> The last value in indexToTerms is going to be ~ tiiFileLength, and if instead you use,
> {quote}int bitEstimate = (int) Math.ceil(Math.log10(tiiFileLength) / Math.log10(2));
> GrowableWriter indexToTerms = new GrowableWriter(bitEstimate, indexSize, false);{quote}
> Load time improves to ~ 2 seconds.

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